The invention pertains to an accessory drive for the valves of an internal combustion engine, especially an Otto engine, especially for a motor vehicle, with at least one camshaft, which is divided into two camshaft halves. A camshaft gear wheel is provided between the two halves of the camshaft.
In internal combustion engines with variable control times achieved by means of an appropriate camshaft adjusting system, the valve opening and/or closing times can be adapted more effectively to the highly dynamic gas exchange process. The advantages of variable control times include above all a gas-exchange loop optimized with respect to losses, improved filling of the cylinders, and the possibility of internal exhaust gas return in the partial-load range by means of a correspondingly large valve overlap.
An accessory drive which has camshaft gear wheels seated on the camshafts in a central position is known from DE 198-40,659 A1.
Accordingly, it is an object of the present invention to provide an accessory drive of the type indicated above with respect to the space it occupies without any loss of performance, so that this drive can also be used in internal combustion engines with a large number of cylinders, such as 18 cylinders, without the need for complicated modifications to the engine itself.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in an accessory drive in which a hydraulic camshaft adjuster is installed between the two halves of the camshaft. The adjuster is designed as a thrust bearing for the two halves of the camshaft. Each half of the camshaft has a hydraulic fluid connection extending via the associated thrust bearing to the camshaft adjuster.
This offers the advantage that, in a simple and low-cost manner, a continuous phase adjustment at a crank angle of at least 40xc2x0 is made available in a small amount of space, so that, on existing engines with center power takeoff, only slight modifications or adaptations are required for the installation of the accessory drive according to the invention. In addition. the hydraulic fluid serves simultaneously as a lubricating medium for the thrust bearings by flowing to, over, and away from them.
So that the amount of space occupied is as small as possible, the camshaft gear wheel is integrated into the camshaft adjuster, and the camshaft adjuster is preferably designed as a vane cell adjuster. The vane cell adjuster has an impeller and a vane cell wheel. The impeller has five or six vanes, and the vane cell wheel has five or six vane cells.
An especially compact and space-saving arrangement without loss of performance can be achieved by providing the vane cell adjuster with the following geometry,: wall thickness, 3 mm; outside diameter, 66 mm; inside diameter, 34 mm to 36 mm; width, 21 mm to 24 mm, and preferably 22 mm; effective area per vane, 315 mm2 to 384 mm2, and preferably 330 mm2, 360 mm2, 336 mm2, or 372 mm2; effective diameter, 25 mm to 26 mm, and preferably 25.5 mm.
In a preferred embodiment, the camshaft adjuster is connected by way of end pieces to each of the two halves of the camshaft, and a hydraulic fluid connection extending between the camshaft half and the camshaft adjuster is provided in each end piece. Here it is preferred for each end piece to be inserted into an interior space in the half of the camshaft. When two end pieces are assigned to a camshaft adjuster, it is advisable for the hydraulic fluid connection to be external for the one end piece and internal for the other.
It should be pointed out that, within the scope of the overall disclosure, the term xe2x80x9ccamshaft halfxe2x80x9d is not meant to signify necessarily an exact geometric division into two identical halves. Instead, the term also covers dimensions for these two parts of a camshaft which do not represent a division into two precisely equal halves.
Regardless of how the end pieces and the camshaft adjuster are arranged, a central screw is provided, which clamps the camshaft adjuster to the associated end pieces installed at the ends.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.